1. Field of the Invention
This invention relates to railroad hopper cars for shipment of a dry granular commodity and particularly to cars having an effective self-contained discharge system, for example fluidizing conveyors in combination with a slide gate discharge assembly which also inhibits contamination of the commodity during shipment and discharge.
2. Prior Art
Use of self-contained unloading devices in a vehicle for transporting bulk commodities is well known. For example, U.S. Pat. No. 2,609,125 discloses a transportable bin with a pair of air activated conveyors to promote unloading of commodity in the bin.
A railroad car with a self-contained unloading device and associated outlet with a closing mechanism is set forth in U.S. Pat. No. 2,789,739. In this case the outlet may be closed or opened by rotation of an arcuate closure plate attached by webs to a hub on a shaft. A gate assembly for use as part of a railroad hopper car outlet is shown in U.S. Pat. No. 2,751,859. The assembly includes a gate having side rack teeth engaging a pinion gear on a handle operated shaft. The gate may be retracted into an enclosable shroud to open the car outlet. The underside of the gate is protected by a cover plate during shipment which then is removed before the car is emptied.
Railroad hopper cars with substantially more sophisticated self-contained unloading means are shown in U.S. Pat. Nos. 3,379,478, 3,469,888 and 4,440,528. In each case a rather elaborate piping arrangement is used to supply a flow of air selectively to a pressurized car body. For example, in the '478 patent air flows through bottom fluidizing conveyors in the car to a top sump where it is then piped downward to a horizontal unloading tube. Air flowing in this tube draws commodity up a downward facing conduit in a bottom sump in the car. In the '888 reference the hopper car bottom has two pairs of fluidizing conveyor troughs. An air flow is alternated to these conveyor troughs to produce like aeration of commodity above the conveyor troughs. The '528 reference also teaches the use of alternating aeration but suggests a different piping arrangement to achieve this result.